Method and system for determining the alignment of a surface of a material in relation to a laser beam

Abstract

The present invention generally relates to a method and system for determining the position and alignment of a plane in relation to an intersecting axis and using that known position and alignment to allow for corrections to be made when using the plane as a reference plane. More particularly, the invention relates to a method and system for determining the angle of tilt of a planar surface in relation to a laser beam, and using the determined angle of tilt to calculate a correction factor to be applied to the laser beam. Briefly stated, the method and system ultimately calculates a correction factor, z-offset, that is applied when using the laser beam in a procedure.

1. A method for determining the position and alignment of a surface of an object in relation to a laser beam, the method comprising the steps of:
 providing an object having a substantially planar surface; 
 providing a laser system for generating a laser beam; 
 repeatedly moving a focal point of the laser beam along a predetermined pattern in a plane perpendicular to a z-axis of the laser beam; 
 detecting at least one plasma spark when the laser beam focal point contacts the object; and 
 determining the alignment of the planar surface in relation to the laser beam. 
 
     
     
       2. The method of  claim 1 , wherein the laser beam is formed of a continuously repeating train of short optical pulses in the range of femtoseconds or picoseconds. 
     
     
       3. The method of  claim 1 , wherein the object is an aplanation lens, glass plate, or microscope slide. 
     
     
       4. The method of  claim 1 , wherein the object is comprised of glass, silicon, plastic, or biologic material. 
     
     
       5. The method of  claim 1 , wherein the moving step comprises:
 setting the focal point of the laser beam at a starting point on a z-axis plane such that the focus of the laser beam is not in contact with the object; 
 repeatedly moving the focal point of the laser beam along a predetermined pattern in a plane perpendicular to the z-axis; and 
 after an occurrence of the completion of movement of the laser beam along the predetermined pattern, repositioning the focal point of the laser beam on the z-axis a set distance Δz from his previous z-axis. 
 
     
     
       6. The method of  claim 1 , wherein the predetermined pattern is circular. 
     
     
       7. The method of  claim 5 , wherein the detecting step comprises:
 identifying a first plasma spark when the laser beam comes into contact with the object, 
 recording the a first z-axis location of the first plasma spark; 
 identifying the completion of the predetermined pattern by identifying a second plasma spark along the complete predetermined pattern; and 
 recording a second z-axis location of the second plasma spark. 
 
     
     
       8. The method of  claim 7 , wherein the determining step comprises:
 calculating the alignment of the object in relation to the z-axis using the first z-axis location and the second z-axis location. 
 
     
     
       9. The method of  claim 8 , wherein the calculation utilizes the formula θ=tan −1 (Δz/D) where θ is the angle between an aplanation lens and a plane perpendicular to the z-axis, and wherein Δz is the difference between the first z-axis location and the second z-axis location, and D is the diameter of the predetermined pattern. 
     
     
       10. The method of  claim 1 , wherein the detecting step comprises:
 providing a video camera for taking images of the object; and 
 capturing a series of images of the object. 
 
     
     
       11. The method of  claim 10 , wherein the detecting step comprises:
 comparing said images of the object to determine the occurrence of at least one plasma spark. 
 
     
     
       12. The method of  claim 1 , wherein the determining alignment step comprises:
 calculating a first image pixel value and a second image pixel value; and 
 calculating a total compared pixel value by subtracting the first image pixel value from the second image pixel value. 
 
     
     
       13. The method of  claim 12 , wherein the determining alignment step further comprises:
 plotting the total compared pixel value to establish a plasma spark line. 
 
     
     
       14. The method of  claim 1 , wherein the detecting step comprises:
 providing a photodetector for detecting plasma sparks; and 
 identifying the occurrence of the plasma spark with the photodetector. 
 
     
     
       15. The method of  claim 14 , wherein the photodetector is any one of a photodiode, CCD, photomultiplier, or phototransistor. 
     
     
       16. The method of  claim 1 , wherein the detecting step comprises manually detecting the occurrence of a first plasma spark and the occurrence of a second plasma spark at the completion of a predetermined pattern. 
     
     
       17. The method of  claim 1 , wherein the determination step determines the tilt of the planar surface of the object in relation to the laser beam. 
     
     
       18. The method of  claim 1 , wherein the detecting step includes measuring a voltage differential generated by a photodetector. 
     
     
       19. The method of  claim 1 , wherein the object is clear or opaque. 
     
     
       20. A laser system for determining the position and alignment of a surface of an object relative to a laser beam generated from the laser system, the system comprising:
 a laser system for generating a laser beam, the laser system having a central processing unit, the central processing unit configured for instructing movement of the laser beam; 
 a plasma spark detection device for detecting a plasma spark, the plasma spark detection device interconnected with the laser system; and 
 a software program for execution on the central processing unit, the software program configured for:
 repeatedly moving a focal point of the laser beam along a predetermined pattern in a plane perpendicular to a z-axis of the laser beam; 
 detecting a plurality of plasma sparks when the laser beam focal point contacts the surface of the object; and 
 determining the position and alignment of the surface in relation to the laser beam. 
 
 
     
     
       21. The system of  claim 20 , wherein the plasma spark detection device is a photodetector. 
     
     
       22. The system of  claim 21  wherein the photodetector is any of a photodiode, CCD photomultiplier, or phototransistor. 
     
     
       23. The system of  claim 21 , wherein the plasma spark detection device is a video camera. 
     
     
       24. The system of  claim 20 , wherein laser beam is formed of a continuously repeating train of short optical pulses in the range of femtoseconds or picoseconds. 
     
     
       25. The system of  claim 20 , wherein the software for the moving step is configured for:
 setting the focal point of the laser beam at a starting point on a z-axis plane such that the focus of the laser beam is not in contact with the object; 
 repeatedly moving the focal point of the laser beam along a predetermined pattern in a plane perpendicular to the z-axis; and 
 repositioning the focal point of the laser beam on the z-axis a set distance Δz from the previous z-axis. 
 
     
     
       26. The system of  claim 20 , wherein the predetermined pattern is a circular. 
     
     
       27. The system of  claim 20 , wherein the software for the detecting step is configured for:
 identifying a first plasma spark when the laser beam comes into contact with the object, 
 recording the a first z-axis location of the first plasma spark; 
 identifying the completion of the predetermined pattern by identifying a second plasma spark along the complete predetermined pattern; and 
 recording a second z-axis location of the second plasma spark. 
 
     
     
       28. The system of  claim 27 , wherein the software for the determining step as configured for:
 calculating the alignment of the object in relation to the z-axis using the first z-axis location and the second z-axis location. 
 
     
     
       29. The system of  claim 28 , wherein the software for the calculation utilizes the formula θ=tan −1 (Δz/D) where θ is the angle between an aplanation lens and a plane perpendicular to the z-axis, and wherein Δz is the difference between the first z-axis location and the second z-axis location, and D as the diameter of the predetermined pattern. 
     
     
       30. The system of  claim 23 , wherein the software for the detecting step is configured for:
 capturing a first and second image of the object. 
 
     
     
       31. The system of  claim 30 , wherein the software for the determining alignment step is configured for:
 calculating a first image pixel value and a second image pixel value; and 
 calculating a total compared pixel value by subtracting the first image pixel value from the second image pixel value. 
 
     
     
       32. The system of  claim 21 , wherein the software for the detecting step is configured for:
 identifying the occurrence of the plasma spark with a photodetector. 
 
     
     
       33. The system of  claim 20 , wherein the software for the detecting step is configured for:
 receiving input from an input device to signal the occurrence of a first plasma spark and the occurrence of a second plasma spark at the completion of the predetermined pattern. 
 
     
     
       34. The system of  claim 33 , wherein the input device is a footswitch. 
     
     
       35. The system of  claim 20 , wherein the software for the determination step is configured for:
 determining the tilt of the planar surface of the object in relation to the laser beam. 
 
     
     
       36. A method for determining the alignment of a surface of an object in relation to a laser beam, the method comprising the steps of:
 providing an object having a substantially planar surface; 
 providing a laser system for generating a laser beam; 
 identifying at least three points at the surface of the object by detecting the occurrence of plasma spark; and 
 determining the tilt of the planar surface in relation to a z-axis of the laser beam. 
 
     
     
       37. A laser system for determining the position and alignment of a surface of an object relative to a laser beam generated from the laser system, the system comprising:
 a laser system for generating a laser beam, the laser system having a central processing unit, the central processing unit configured for instructing movement of the laser beam; 
 a plasma spark detection device for detecting a plasma spark, the plasma spark detection device interconnected with the laser system; and 
 a software program for execution on the central processing unit, the software program configured for:
 identifying at least three points at the surface of the object by detecting the occurrence of plasma spark; and 
 determining the tilt of the planar surface in relation to a z-axis of the laser beam utilizing the at least three points. 
 
 
     
     
       38. A method for determining the focus of a laser beam about a surface of an object, the method comprising the steps of:
 providing an object having a substantially planar surface; 
 providing a laser system for generating a laser beam; 
 monitoring a nonlinear interference frequency signal generated by the laser beam while scanning a z-axis depth of the focal point relative to the object, wherein the nonlinear interference frequency signal results from interaction between the focal point of the laser beam and the object and has a quadratic or higher order dependence on an intensity of the laser beam; and 
 determining whether the focal point of the laser is at the surface of the object. 
 
     
     
       39. The method of  claim 38 , wherein the signal is any one of second harmonic generation, third harmonic generation, stimulated Raman, or white light generation and others. 
     
     
       40. A laser system for determining the focus of a laser beam about a surface of an object the system comprising:
 a laser system for generating a laser beam, the laser system having a central processing unit, the central processing unit configured for instructing movement of the laser beam; 
 a photomultiplier with a band pass filter for detecting a nonlinear interference frequency signal generated by the laser beam, wherein the nonlinear interference frequency signal results from interaction between the focal point of the laser beam and the object and has a quadratic or higher order dependence on an intensity of the laser beam; and 
 a software program for execution on the central processing unit, the software program configured for:
 monitoring the nonlinear interference frequency signal detected by the photomultiplier while scanning a z-axis depth of the focal point relative to the object; and 
 
 determining whether the focal point of the laser is at the surface of the object using the quadratic or higher order dependence of the nonlinear interference frequency signal on the intensity of the laser beam. 
 
     
     
       41. The system of  claim 40 , wherein the signal is any one of second harmonic generation, third harmonic generation, stimulated Raman, or white right generation and others. 
     
     
       42. A method for determining the distance between two surfaces utilizing a laser beam, the method comprising the steps of:
 providing a first object having an outer surface; 
 providing a second object having an outer surface; 
 providing a laser system for generating a laser beam; 
 identifying a first coordinate position of a first point at the outer surface of the first object by detecting the occurrence of a first plasma spark; 
 identifying a second coordinate position of a second point at the outer surface of the second object by detecting the occurrence of a second plasma spark; and 
 determining the distance between the first point and the second point. 
 
     
     
       43. A laser system for determining the position and alignment of a surface of an object relative to a laser beam generated from the laser system, the system comprising:
 a laser system for generating a laser beam, the laser system having a central processing unit, the central processing unit configured for instructing movement of the laser beam; 
 a plasma spark detection device for detecting a plasma spark, the plasma spark detection device interconnected with the laser system; and 
 a software program for execution on the central processing unit, the software program configured for:
 identifying a first coordinate position of a first point at the outer surface of a first object by detecting the occurrence of a first plasma spark; 
 
 identifying a second coordinate position of a second point at the outer surface of the second object by detecting the occurrence of a second plasma spark; and 
 determining the distance between the first point and the second point.